In my book I argue that there is no coherent understanding of the atonement. Here are some questions for those who accept the penal substitutionary view:

In order for someone to be forgiven why must there be punishment at all? We know of victims who have forgiven their assailants even though they have never been punished, and we know of other victims who won't forgive their assailants even after they have been punished. To forgive someone doesn't mean that you must first punish the offender at all. Forgiveness doesn't really depend upon the remorse of the offender, either, although it does help quite a bit. At this point it's not up to the offender at all, but the victim who must find a way to forgive.

To forgive means bearing the suffering of what that person has done to you without retaliation. If I stole something from you, then forgiveness means bearing the loss without recompense. If I slandered you, forgiving means bearing the humiliation without retaliating. If the cross of Christ means someone got punished for my sins, then that's not offering forgiveness, that's punishing someone for what I did wrong.

If the cross was needed to pay the punishment for my sins, then how can God really be a forgiving God? Forgiveness doesn't require punishment. To put it bluntly, if I can't forgive you for striking me on the chin until I return the blow back to you, or to someone else, then that's not forgiveness, that's retaliation, or sweet revenge! Revenge is never an ethical motive for action, even if we are led to take revenge on others sometimes. John Hick: "A forgiveness that has to be bought by the bearing of a just punishment is not forgiveness, but merely and acknowledgment that the debt has been paid in full. (The Metaphor of God Incarnate, p. 127).